The present invention relates to cartridges used in supplying liquid ink to a printhead in a thermal ink jet printing apparatus.
Thermal ink jet printing is well understood in the art. U.S. Pat. No. 5,997,121 describes several aspects of such printing.
In existing thermal ink jet printing, the printhead comprises one or more ink filled channels communicating with a relatively small supply chamber, or manifold, at one end, and having an opening at the opposite end, referred to as a nozzle. In current practical embodiments of drop on demand thermal ink jet printers, it has been found that the printers work most effectively when the pressure of the ink in the printhead nozzle is kept within a predetermined range of gauge pressures. Specifically, at those times during operation in which an individual nozzle or an entire printhead is not actively emitting a droplet of ink, it is important that a certain negative pressure, or "back pressure", exist in each of the nozzles and, by extension, within the ink supply manifold of the printhead. The attributes of creating and maintaining such back pressure are described in the U.S. Pat. No. 5,289,212, the contents of which are incorporated herein by reference.
The ink is supplied to the printhead from an ink cartridge. The ink cartridge contains a supply of ink, and is typically configured to maintain the required negative pressure. The ink cartridge is typically a user-replaceable unit that mates with the printhead of the printing apparatus.